1. Field of the Invention
The present invention is related to a multi-optical axis photoelectric sensor configured by light emitting and receiving units each of which is formed by disposing a plurality of light emitting or receiving elements in a line to form a light curtain between them for detecting an object like a human body entering into the light curtain, and is especially related to an indicator installed into the multi-optical axis photoelectric sensor.
2. Description of the Related Art
To secure the safety of human being from a machine that is a hazardous source, like a press machine, a multi-optical axis photoelectric sensor is provided to the route where human being can enter into such a hazardous source.
A multi-optical axis photoelectric sensor has a light emitting unit having a plurality of light emitting elements disposed along a longitudinal direction of the unit in a line and a light receiving unit having a plurality of light receiving elements disposed along a longitudinal direction of the unit in a line.
A light curtain is formed by a plurality of light axes formed between the light emitting and receiving units. When some object intrudes into the light curtain, the sensor detects blocking of some of the light axis of the light curtain and outputs a cutout order signal for stopping a power source of a motor for driving the hazardous source so as to maintain a safety by stopping the operation of the hazardous source forcibly.
In general, a multi-optical axis photoelectric sensor uses an infrared ray as the light emitted by the light emitting element. In this case, since the infrared ray is invisible and the multi-optical axis photoelectric sensor comprises only two elongated casings, it is difficult to visibly position the light curtain.
If an operator can recognize the position of the light axes of the light curtain, it will increase the level of safety of the operation.
In view of the above requirement, it has already been proposed that a multi-optical axis photoelectric sensor has a plurality of indicators disposed at a side surface being different from a front surface of a casing for emitting the light or receiving the light.
However, in this conventional technology, when the casing of the light emitting or light receiving unit is covered by a protecting cover made of some metal to protect the sensor or to reinforce the sensor, the indicators are also covered by the cover except for the light emitting or light receiving surface and therefore becomes invisible for an operator.
Further, for example JP-A-1999-345548 and corresponding U.S. Pat. No. 6,414,603 describe a light emitting unit of a multi-optical axis photoelectric sensor having a plurality of indicating elements along a longitudinal direction of the unit across an approximately total length of the unit.
However, since the optical axes and the indicating elements are facing to outside of the unit through a light emitting surface and are parallel with each other along the longitudinal direction, a width of the light emitting surface becomes wider in a transverse direction of the unit.
Further, since an axis including the plurality of the indicating elements disposed along the longitudinal direction is offset to the optical axes disposed along the longitudinal direction, it is difficult for an operator to recognize an exact plane having the light curtain.